The prevention of infectious diseases in older adults remains a major public health challenge, as acute respiratory infections are a leading cause of hospitalisation, mortality, and functional decline worldwide. Immunosenescence and environmental exposures increase susceptibility to infection and reduce vaccine effectiveness in this population. Respiratory viruses, including influenza, SARS-CoV-2, respiratory syncytial virus, and human metapneumovirus, account for a substantial share of this burden, much of which is vaccine-preventable. However, their impact on functional decline and recovery in older adults remains insufficiently characterized. This international study aims to assess the effect of hospitalization for major respiratory viral infections on loss of autonomy in individuals aged 60 years and older, to inform targeted prevention and vaccination strategies.

The prevention of infectious diseases in older adults represents a major public health challenge due to their substantial impact on morbidity, mortality, and loss of functional capacity. Acute respiratory infections are among the leading causes of hospitalization and death in this population worldwide.

Ageing is associated with a progressive decline in immune function, resulting in increased susceptibility to infections and reduced vaccine effectiveness. In addition, environmental factors such as residence in collective living settings and repeated exposure to healthcare environments further increase the risk of exposure to and transmission of infectious agents.

The pathogens most frequently involved include respiratory viruses namely influenza, SARS-CoV-2, respiratory syncytial virus, and human metapneumovirus as well as bacterial pathogens, particularly Streptococcus pneumoniae, and certain fungal agents. A substantial proportion of these infections are potentially preventable through vaccination.

Despite advances generated by the European IMI VITAL project and the AEQUI case-control study, data remain limited regarding the functional consequences of acute respiratory infections in older adults, particularly their impact on dependency, frailty, and post-infectious recovery.

This international study aims to address these knowledge gaps by evaluating the impact of hospitalizations related to influenza, SARS-CoV-2, respiratory syncytial virus, and human metapneumovirus on loss of autonomy in individuals aged 60 years and older. The findings are expected to strengthen the scientific evidence base needed to inform targeted vaccination and prevention strategies, ultimately contributing to healthier ageing.

Inclusion Criteria:

• Male or female subjects aged 60 years or older
• Hospitalized in a study center (emergency department, infectious disease, internal medicine or geriatric hospital wards…) for acute respiratory infection (refer to table 1 below for definition).
• Confirmed positive PCR test for influenza, SARS-CoV-2, RSV, or human metapneumovirus (hMPV). Participants with co-infections with other viral or bacterial agents can be included.

Exclusion Criteria:

• Participants with conditions significantly impacting short-term functional status, such as severe disability (ADL score ≤2 or Clinical Frailty Scale ≥7), terminal illness, palliative care needs, or inability to comprehend and complete study questionnaires due to severe stroke sequelae, complete sensory loss, advanced dementia, or similar impairments.
• Participants that refuse or are unable to answer the 3- and 6-months follow-up phone call assessments
• Positive laboratory test for single (mono-infection) virus other than influenza, SARS-CoV-2, RSV, or human metapneumovirus (HMPV)
• Participant in exclusion period for another study using an investigational / unapproved medicinal product.
• Participant referred to in articles L1121-5 to L1121-8 of the CSP (corresponding to all protected persons : pregnant woman, parturient, breastfeeding mother, person deprived of liberty by judicial or administrative decision, persons undergoing psychiatric care under articles L.3212-1 and L.3213-1 who do not fall under article L.1121-8, persons admitted to a healthcare or social institution for purposes other than research, minors, person under legal protection or unable to express consent).
• Individuals opposed to participating in the research
• Staff members with a hierarchical relationship to the principal investigator

The study population will include participants aged 60 years or older who are hospitalized with a serious acute respiratory infection in the departments of infectious diseases, geriatrics, internal medicine, pulmonology, or emergency medicine. Recruitment will be conducted by investigator physicians in each participating department. Potentially eligible participants will be identified by daily screening of admission records and results from standard of care respiratory samples.

Each country will aim to recruit approximately 320 participants - 80 with each pathogen of interest. Efforts will be made to secure an equal distribution of participants aged 60-75 and >75 years age.